Summary of work: Studies in our laboratory concerning the adenosine receptor system have expanded into several areas. We have described a specific binding site for [3H] nitrobenzylthioinosine ([3H] NBI) which probably represents the adenosine reuptake site. This site has a distinct pharmacology from that of the adenosine receptor. The interaction of caffeine with the adenosine and benzodiazepine receptor in human brain has been studied. The relationship of the calcium channel with adenosine receptors has also been studied. The binding of the calcium antagonist [3H] nitrendipine, [3H] NDP has been characterized with evidence generated showing that this compound is binding to the calcium channel. Behavioral studies have shown that the metabolically stable adenosine analogues cyclohexyladenosine and 2-chloroadenosine are extremely potent as sedatives and tranquilizers. Autoradiographic studies have also revealed that the adenosine receptor has a heterogeneous distribution in brain. The effect of Adenosine on l4C 2-deoxyglucose uptake is also being studied in an attempt to correlate these metabolic effects with receptor distribution and to identify functional receptors.